M3 won't turn on laser

Machine is Genmitsu 3018 with 5.5k laser. Laser will turn on with switch, but not with M3 command. The rest of the code runs fine.
$32=1 $30=1000. Grbl 1.1f. When I use lasergrbl with the laser manually switched on, the laser turns offwhen it should be on, and on when it should be off. With Lightburn, there is no response to any m3/4/5 codes. Sainsmart replaced the laser, but I get the same results.
Please help.

When you enter M3 the laser doesn’t switch on immediately. You have to enter the G1 state, and give an S command with a value from 1 to 1000, like this:

G1 S50 ; 5% power, assuming 0 to 1000

Then G1 S0 to set the power back to zero, and/or M5 to turn it off.

If you’re using the ‘GRBL’ driver instead of GRBL-M3, the laser will scale the power output if it’s not allowed to move as fast as requested, and SainSmart has the speed limits set very low by default. If you’re using LightBurn in mm/sec mode instead of mm/min mode, this can add confusion, and make it appear the laser is not firing, or is very weak.

Look at $110 / $111 here: https://github.com/gnea/grbl/wiki/Grbl-v1.1-Configuration

And look at the LightBurn Edit > Settings to make sure you’re in mm/min (better for diode) mode.

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